The present disclosure relates to turbine engines, and more particularly, to flow control and inter-turbine duct assemblies for use in turbine engines. In gas turbine engines, there is a preferred ratio between the diameters of the high-pressure turbine spool and the low-pressure turbine spool. Specifically, the low-pressure turbine spool has a larger diameter than the high-pressure turbine spool to provide optimal engine performance. Because of this difference in radial size, the transition duct joining the high-pressure and low-pressure turbines must accommodate this change in radius.
However, increasing the size of the duct over a relatively short distance can result in boundary layer separation of the flow within the duct, adversely affecting low-pressure turbine performance. Therefore, gas turbine engines are often designed with elongated transition ducts, or transition ducts that do not achieve the optimal ratio between the high-pressure turbine size and the low-pressure turbine size.
Fluidic flow control from a single slot, typically located at the inlet of a diffusing transition duct, has been used to deliver high momentum fluid to prevent boundary layer flows from separating along the walls of an aggressive, high area-ratio inter turbine duct. The total momentum of injection flow must be sufficient to keep the boundary layers attached along the entire length of the duct. However, large total momentum induces a penalty on the engine cycle because it is typically bled from other sections of the engine (e.g. compressor) and reduces their performance. It is useful then to minimize the total momentum of injected flow required to prevent separation in an aggressive high-area-ratio transition duct.
Therefore, there is a need for continued improvement in the design of such inter-turbine transition ducts that minimize the total momentum of injected flow.